Heretofore, in the medical and printing plate-making fields, effluent generated by the wet process of image forming materials has resulted in problems for workability. In recent years, it has increasingly been demanded to reduce the processing effluent in view of environmental protection and space saving. Accordingly, silver salt photothermographic dry imaging materials capable of forming images by application of only heat have been practiced and increasingly employed in the aforesaid fields. Silver salt photothermographic dry imaging materials themselves (hereinafter referred to as heat developable materials or simply as light-sensitive materials) were proposed a relatively long time ago (refer, for example, to Patent Documents 1 and 2).
However, it has been difficult to disperse, into organic solvents, conventional light-sensitive silver halide grains which are prepared employing gelatin as a protective colloid. As a result, it has been difficult to mix the above grains with polymers dissolved in organic solvents or organic silver particles dispersed in organic solvents. On account of that, it has been required that light-sensitive silver halide grains are previously mixed during a process in which organic silver salts are prepared in an aqueous system and after drying, organic silver particles are dispersed into organic solvents. Due to that, when a relatively large force is applied to the dispersion of organic silver salts, silver halide grains are damaged, whereby problems occur in which restrictions are applied to dispersion of organic silver salts.
An example is proposed in which silver halide grains are prepared employing synthetic hydrophilic polymers instead of gelatin and polymers having an amino group are employed so that the resulting silver halide grains can be dispersed into organic solvents. However, the use of such an amino group accelerates Ostwald ripening of silver halide, and it becomes difficult to decrease the size of silver halide grains. In addition, by making the amino group hydrophobic, grains are subjected to sedimentation, whereby desalting is carried out. In order to do so, it is necessary to raise the pH to at least 8, whereby problems occur in which fog of silver halide grains increases. As a result, in practice, the above proposal has not been suitable as a means to enhance photographic speed, to retard fog, and to improve silver color tone (refer, for example, to Parent Documents 3 and 4).
(Patent Document 1)U.S. Pat. No. 3,152,904(Patent Document 2)U.S. Pat. No. 3,457,075(Patent Document 3)Japanese Patent Publication Open toPublic Inspection (hereinafterreferred to as JP-A) No. 47-9179(Patent Document 4)U.S. Pat. No. 3,748,143